[Nescafe]

Hi,

The only difference between the two is that 13C has an extra neutron. How is it that try said 13C has a spin of 1/2, what does it even mean? Don't they have the same number electrons?

Nescafé.

[gippgig]

All carbon atoms have 6 electrons with an overall electron spin (all spins given here are for the ground state; excited states can vary) of zero. The nuclear spin is different for different isotopes; the nucleus of ¹²C has a spin of 0 while the nucleus of ¹³C has a spin of 1/2.

[Nescafe]

All carbon atoms have 6 electrons with an overall electron spin (all spins given here are for the ground state; excited states can vary) of zero. The nuclear spin is different for different isotopes; the nucleus of ¹²C has a spin of 0 while the nucleus of ¹³C has a spin of 1/2.

But why, what does that even mean to have a spin of 1/2, the only difference is a neutron extra in 13C v.s. 12C. How come they have different spins?

Nescafe.

[fledarmus]

I don't know if you have the background to understand the answer, but you can find an "elementary" discussion of it here.

http://en.wikipedia.org/wiki/Nuclear_spin

In terms of NMR spectroscopy, you can think of protons and neutrons having opposite spins. If you have equal numbers of protons and neutrons in the nucleus, the spins will cancel and the nucleus will have no magnetic moment. If there is no magnetic moment, the magnet of the NMR will have no effect on the population of spin states, and the nucleus will be invisible to NMR. This includes C12, N14, deuterium, and many oyher isotopes. On the other hand, C13, protons, and N15 for example have different numbers of protons and neutrons, and therefore the population of spin states can be affected by magnetic fields and the nucleus will show a signal in the NMR.

[Nescafe]

I don't know if you have the background to understand the answer, but you can find an "elementary" discussion of it here.

http://en.wikipedia.org/wiki/Nuclear_spin

In terms of NMR spectroscopy, you can think of protons and neutrons having opposite spins. If you have equal numbers of protons and neutrons in the nucleus, the spins will cancel and the nucleus will have no magnetic moment. If there is no magnetic moment, the magnet of the NMR will have no effect on the population of spin states, and the nucleus will be invisible to NMR. This includes C12, N14, deuterium, and many oyher isotopes. On the other hand, C13, protons, and N15 for example have different numbers of protons and neutrons, and therefore the population of spin states can be affected by magnetic fields and the nucleus will show a signal in the NMR.

Ahh I see, that is the answer I was looking for. Makes sense!

Thank you sir!

Nescafe.

[gippgig]

Oops. I made an invalid assumption. I'm not certain that the electron spin of a carbon atom is zero. It's either 0 or 1.